Android 获得图片并解码成缩略图以减少内存消耗
本文内容
- 环境
- 演示
环境
- Windows 2008 R2 64 位
- Eclipse ADT V22.6.2，Android 4.4.3
- SAMSUNG GT-I9008L，Android OS 2.2.2
演示
缩略图能减少手机内存的消耗。网络上的资源一般对手机来说，大了点，把图片解码，减少其尺寸，从而减少手机内存的消耗。
本文采用的歌曲列表是 Android_Music_Demo_json_h_array.xml 文件，虽然文件后缀名是 .xml，但内部其实是 JSON 格式，因为 cnblog 不让上传 .json 格式的文件，该文件里的缩略图都较大，是 .jpg 格式，而与之对应的 Android_Music_Demo_json_array.xml 文件里的缩略图，都很小，都是才不到10k的 .png 格式。
图 1
假设给定一个图片链接地址，想获得图片缩略图，核心代码如下所示，点击此处下载：
private Bitmap getBitmap(String url) {
File f = fileCache.getFile(url);
// from SD cache
Bitmap b = decodeFile(f);
if (b != null)
return b;
// from web
try {
Bitmap bitmap = null;
URL imageUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) imageUrl
.openConnection();
conn.setRequestMethod("GET");
// Sets the flag indicating whether this URLConnection allows input.
// conn.setDoInput(true);
conn.setConnectTimeout(3000);
conn.setReadTimeout(3000);
// Flag to define whether the protocol will automatically follow
// redirects or not.
conn.setInstanceFollowRedirects(true);
int response_code = conn.getResponseCode();
if (response_code == 200) {
InputStream is = conn.getInputStream();
OutputStream os = new FileOutputStream(f);
StreamUtils.CopyStream(is, os);
os.close();
conn.disconnect();
bitmap = decodeFile(f);
return bitmap;
} else {
conn.disconnect();
return null;
}
} catch (Throwable ex) {
ex.printStackTrace();
if (ex instanceof OutOfMemoryError)
memoryCache.clear();
return null;
}
}
private Bitmap decodeFile(File f) {
try {
// decode image size
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
FileInputStream stream1 = new FileInputStream(f);
BitmapFactory.decodeStream(stream1, null, o);
stream1.close();
// Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE = 70;
int width_tmp = o.outWidth, height_tmp = o.outHeight;
int scale = 1;
while (true) {
if (width_tmp / 2 < REQUIRED_SIZE
|| height_tmp / 2 < REQUIRED_SIZE)
break;
width_tmp /= 2;
height_tmp /= 2;
scale *= 2;
}
// decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize = scale;
FileInputStream stream2 = new FileInputStream(f);
Bitmap bitmap = BitmapFactory.decodeStream(stream2, null, o2);
stream2.close();
return bitmap;
} catch (FileNotFoundException e) {
} catch (IOException e) {
e.printStackTrace();
}
return null;
}